This invention relates to structurally strengthened thermoplastics.
Wood has long been a favorite building material. Wood is also commonly used in the manufacture of products such as decorative moldings and frames, and window coverings such as window shutters, and wooden blind slats. Consumers prefer wooden window blind slats and wooden window shutter louvers to plastic, because wooden slats and louvers are light in weight, relatively high in strength and do not significantly bend or sag or decompose upon prolonged exposure to sunlight. Although in great demand, wooden window blind slats and such are not affordable to many consumers. The same is true for many other wood products such as frames and moldings. The high cost of wood and its labor intensive processing hampered the more widespread use of these products. There is a long felt need to find low cost alternatives to wood, with some of the desirable properties of wood.
U.S. Pat. No. 6,083,601 (Prince), for which applicant is a co-inventor, discloses a Venetian blind slat formed of a dried wood byproduct (cellulose, or wood powders) and plastic. The slats of this patent can be difficult and expensive to prepare because cellulose requires time consuming and expensive drying.
Therefore, there is a need to find another alternative to the use of powdered wood to create a strengthened plastic.
The present invention meets that need. The invention is directed to articles containing a thermoplastic strengthened with a porous siliceous material, such as dried diatomaceous earth, and processes for making such articles. The invention is especially useful for thermoplastic window covering products, such window blind slats, and window shutter components such as shutter louvers, shutter stiles, and shutter frames.
According to the invention, the article can be made of a closed cell foam thermoplastic or a substantially solid thermoplastic (not foam) strengthened with diatomaceous earth containing no more than about 2% by weight of moisture. Thus, a dried or powdered diatomaceous earth is used to form the article.
A preferred embodiment of the invention is an article that comprises a closed cell foam of a first thermoplastic, containing between about 1% and 40% of powdered diatomaceous earth by weight. The article is formed with diatomaceous earth containing no more than about 2% by weight of moisture. Preferably the article comprises between about 1% and about 40% by weight of diatomaceous earth, more preferably between about 5% and about 30%, and most preferably between about 10% and about 25%.
In another preferred embodiment of the invention, the article is a substantially solid article that comprises a first thermoplastic, containing between about 1% and 70% of powdered diatomaceous earth by weight, the article being formed with diatomaceous earth containing no more than about 2% by weight of moisture; more preferably the diatomaceous earth content is between about 5% and about 55% by weight of diatomaceous earth, most preferably between about 10% and about 40%.
Optionally, whether closed cell foam thermoplastic or substantially solid thermoplastic is the component, the article can be at least partially surrounded by a co-extruded protective cladding of a second thermoplastic. The first and second thermoplastic can be either the same or can be different, but preferably must be compatible with each other so that they can be co-extruded. The article surrounded and at least partially enclosed by a protective cladding will have weight, strength and rigidity characteristics comparable to the characteristics of similarly dimensioned wooden products. This article enclosed by a protective cladding will perform comparably to wood when exposed for extended periods to heat and sunshine.
Preferebly, specially where the article is not co-extruded with a protective cladding, a UV protectant such as titanium dioxide can be added to the thermoplastic before the extrusion of the article, in a preferred range of between about 1% to about 10% by weight of powdered titanium dioxide, more preferably between about 4% to about 7% by weight, and most preferably between 5% to about 6% by weight.
The article preferably contains sufficient diatomaceous earth so that the article flexural strength and flexural modulus are each greater than that of another substantially identical article without the diatomaceous earth; preferably the article contains sufficient diatomaceous earth so that its flexural strength is at least about 50% greater than that of another substantially identical article without the diatomaceous earth; preferably the article contains sufficient diatomaceous earth so that its flexural modulus is at least about 50% greater than that of another substantially identical article without the diatomaceous earth; more preferably the article contains sufficient diatomaceous earth so that the article has flexural strength and flexural modulus that are each at least about 100% greater than that of another substantially identical article without the diatomaceous earth, most preferably at least about 200% greater.
Preferably the article has an apparent density lower than 1 gm/cu. cm., more preferably less than about 0.8 gm/cu. cm., and most preferably less than about 0.65 gm/cu. cm., but no less than about 0.3 gm/cu. cm.
Preferably, the diatomaceous earth used in forming the article is sized in the range of about 50-700 standard U.S. mesh, more preferably in the range of 200-400 standard U.S. mesh, and most preferably with at least about 90% of the diatomaceous earth being finer than 300 standard U.S. mesh.
Preferably, the diatomaceous earth used in forming the article is dried by heating it to a temperature sufficiently high to cause the degradation of cellulose based materials, but substantially below the calcining temperatures of diatomaceous earth; preferably the diatomaceous earth is heated to above 230 degrees Fahrenheit, more preferably to above 300 degrees Fahrenheit, even more preferably to a temperature between about 350 degrees Fahrenheit to about 400 degrees Fahrenheit. Preferably, the diatomaceous earth contains less than about 0.5% moisture, more preferably less than about 0.20% moisture, even more preferably less than 0.10% moisture, and most preferably less than about 0.05% moisture. Preferably the first thermoplastic contains no more than about 2% by weight of moisture before the extrusion of the article.
A preferred embodiment for forming thermoplastic foam articles or products can be prepared by (a) mixing a first thermoplastic material with powdered diatomaceous earth, so that the diatomaceous earth content is between about 1% and about 40% by weight; and (b) extruding the resulting mixture to form a thermoplastic closed cell foam with at least a 50% volume expansion of the thermoplastic, to form the product. Preferably the diatomaceous earth is dried to less than about 2% moisture before mixing, more preferably performed by pre-drying the diatomaceous earth to less than about 2% moisture before mixing it with the first thermoplastic material, even more preferably to less than about 0.5% moisture, most preferably to less than about 0.1% moisture.
Preferably the first thermoplastic, when extruded to form a thermoplastic foam, is expanded at least about 50%, more preferably at least about 75%, even more preferably at least about 100%, most preferably at least about 150%, but generally not more than about 400%.
Preferably the thermoplastic foam is formed at least in part of recycled plastics; more preferably the recycled plastic is recycled from the articles or products previously prepared by the method of this invention. The article of this invention can be used to make window covering products, and can be, for example, window blind slats, and components and parts for making window shutters, such as louvers, stiles, and frames and moldings.
The powdered diatomaceous earth is typically dried at a temperature higher than that which can be used with wood. Preferably, the mixing step includes mixing the dried diatomaceous earth with the thermoplastic resin, a coupling agent, and a fatty acid to yield a first mixture. The first mixture is compressed, heated and extruded to form a pelletized and extrudable compound. Moisture is extracted from the powdered diatomaceous earth and the thermoplastic resin at one or more points during the process, to ensure that the ultimate moisture content of the pelletized compound is less than about two percent, more preferably less than about 0.2 percent, even more preferably less than about 0.1%, and most preferably less than about 0.05%.
The above process of making cell foam articles according to the invention also applies when the resulting article is a substantially solid article, and not a closed cell foam article. One exception for substantially solid articles is that the diatomaceous earth content in the substantially solid article product can be relatively higher, and range between about 1% to about 70%, preferably between 5 to 55%, more preferably between 10-40%. One of ordinary skill in the art would understand the modifications necessary to prepare a substantially solid article according to the invention.